AAWSAP DIRD, Biomaterials, January 2010

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Figure 27. Photomicrograph of Titanium Metal (Appears Black in This Photo) in an Intimate Integration
With Living Bone. The intersection of the two materials shows a thin barrier layer and then healthy tissue very
close to the metal. It does not show inflammation or scar tissue formation.
Optimization of the bone integration with titanium has been much studied over the
years. It has been found that if single cells can nestle into pores on the metal surface
and then can reach out and attach to their neighbors, this forms a particularly good
adhesive interface. This observation has led to new types of surface treatments for
titanium to improve its ability to attach to bone. The need for a particular porosity size
scale for optimal bone integration has only recently been recognized.
Sand blasting of the titanium surface has long been done, but, recently, plasma etching
and pitting with the use of acids have been found effective. Some of the more recent
(2008) innovations have been the use of lasers to create a surface modification by
melting pits.
Another good approach is to coat metal implants with bioactive materials, such as
hydroxyapatite (HA) . HA has excellent biocompatibility, bioactivity, and bone-binding
properties. It forms a bond with titania thin films on the surface of titanium implants
and so prepares the surface for adhesion. Researchers recently determined that making
th is layer thick (about 1 micron) encourages cell proliferation and bonding.
Recent improvements in HA have included manufacturing it in the form of a spherical
nanopowder that is more acceptable to tissues than are spicule forms of its natural
occurrence. Using HA in the form of a nanopowder stimulates bone formation leading to
a natural, as well as chemical, adhesion, much like glue.
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